This invention relates to water distribution systems, and in particular to water distribution systems that are able to reliably supply and improve the quality of water throughout a range of external environmental conditions.
The prior art is replete with water distribution systems of various types. Generally, these are once-through systems where water is delivered from a water tank or other source to a user outlet facility such as a tap, but only when a user demand occurs. The path of water flow may include devices such a filters, water purifiers, or the like that are designed to improve the quality of water passing through.
It is also known in prior art water distribution systems to include a means for recirculating stored water for the purpose of aeration and to prevent stagnation. For example, U.S. Pat. No. 5,351,337 granted to Deutsch on Sep. 27, 1994, discloses a system that may be selectively controlled to deliver water from a storage tank to a user outlet facility along a once-through path or, alternately, to recirculate water in a short loop that bypasses a substantial part of the path to facility.
Such systems fail to take full advantage of the benefits that can be achieved with devices such as air and water filters and water purifiers. Further, such systems typically will be quite sensitive to the temperature of the surrounding environment and incapable of operating in freezing temperatures for extended periods without external heating, for example, as is common with many aircraft water distribution systems.
A primary object of the present invention is to provide a method of water distribution and water distribution apparatus that has reduced sensitivity to the temperature of the surrounding environment and that is capable of being operated at freezing temperatures or below for extended periods of time without the need for external heating.
A further object of the present invention is to provide a method of water distribution and water distribution apparatus that is able to improve the quality or impede the deterioration of water, including substantial reduction of organic and inorganic contamination in the system by way of water and air supplied to the system.
In a broad aspect of the method of the present invention, water is supplied to a water user outlet facility by maintaining a tappable flow of water in a recirculating loop that includes a pump that establishes the flow, a water delivery path that extends from the pump to the outlet facility, and a water return path that extends from the outlet facility back to the pump. The flow is permitted to be controllably tapped at the facility by a water user while directing any untapped portion of the flow into the water return path.
The system may include only a single water user outlet facility. However, more typically, it is contemplated that it will include a plurality of such facilities located at intervals around the recirculating loop. In such cases, a part of the water return path for all but the last facility in the loop will also be a part of the water delivery path for the one or more other facilities in the loop.
Two immediate advantages derive from such recirculation. Firstly, recirculation avoids stagnation and thereby impedes deterioration in the potability of the water. The formation of bacteriological colonies is deterred. Secondly, recirculation makes the recirculating loop and water within the loop less sensitive to the temperature of the surrounding environment. In this regard, it will be understood that the operation of the pump effectively adds energy to the system and inherently tends to maintain a continuous and uniform thermal level throughout the system. The added energy to a degree serves to balance heat energy loss to the surrounding environment. Thus, where water in a non-recirculating system will eventually freeze if the system is exposed for a sufficient length of time to freezing temperatures, it may be maintained in a liquid condition in the present system even though the water delivery path, the water return path, or parts thereof, may be so exposed for extended periods. Such avoidance of freezing may be achieved without the necessity to provide external heating for either the water delivery or the water return paths. Of course, there are limits depending upon the volume flow rate that can be maintained by the pump. Harsher environments may dictate a pump that is capable of adding more energy than a pump that would suffice for more moderate environments.
To make the system more adaptable to differing water usage rates, the pump is preferably a centrifugal pump that is driven by a substantially constant speed motor configured to provide a relatively constant discharge pressure over a broad range of water flow rates.
Advantageously, the recirculating loop may include a water purifier such as an ultraviolet lamp source to kill organic contaminants and to impart heat into the water, thus assisting in reducing the probability of freezing in harsh environments. The recirculating loop may also include a filter to remove inorganic material. Preferably, all such devices are located within the water delivery path of the loop and upstream from all water user outlet facilities. While such devices are generally well known in and of themselves, their effectiveness is enhanced by the present system because any given control volume of water may pass through the devices many times before it is ultimately tapped by a user.
In one embodiment of the present invention, the recirculating loop includes a water storage tank in which water is stored as a preliminary step. This embodiment is considered particularly suitable for mobile applications, and especially applications such as airborne applications where the system may be exposed to a wide range of environmental temperatures depending upon flight operations. In airborne operations, the system may be operated whether it takes operating power from the aircraft electrical system while in flight or from ground support facilities while on the ground with the aircraft engines shut down. It is noteworthy that since the water storage tank need not be pressurized as typical in conventional aircraft, it may be shaped or configured to take better advantage of available space within the contours of the aircraft hull.
In another embodiment of the present invention a storage tank is not included. Flow is maintained in the recirculating loop by adding make-up water into the loop to replace water tapped at the user facility or facilities. This embodiment is suited for stationary applications where water is drawn from an external source such as a domestic water supply utility.